1. Field of the Invention
The present invention relates to circuit board material and the method of producing said circuit board material. Specifically, the present invention relates to a circuit board material having an unusually high resistance and a novel electroplating bath, which bath is suitable for use in the production of said circuit board material possessing a high resistance.
2. Prior Art
Methods of forming circuit board material have been described in U.S. Pat. No. 2,662,957 to Eisler; U.S. Pat. No. 3,691,007 to Pavlou; and U.S. Pat. No. 3,808,576 to Castonguay et al. Additionally, improved circuit board material is described in pending U.S. patent application Ser. No. 06/738,835 filed May 29, 1985 by James Rice and assigned to Ohmega Technologies, Inc.
Typically, printed circuit board material consists of an insulating support and an outer layer of conductive material. Alternatively, the printed circuit board material consists of an insulating support layer, one or more layers of electrical resistance material and an outer layer of a conductive material. The printed circuit board stock material is converted into printed circuit boards by selective removal of unwanted layers of conductive material layers or electrical resistance layers.
U.S. Pat. No. 2,662,957 discloses electrical resistance layers comprising manganese and copper, certain copper-manganese-nickel alloys, copper-nickel alloys, nickel-silver alloys, copper-silicon alloys, copper-nickel-chromium alloys, chromium-nickel alloys and chromium-nickel-iron alloys. Additionally, U.S. Pat. No. 2,662,957 describes a general method for manufacturing the printed circuit board stock material and printed circuit boards formed therefrom.
U.S. Pat. No. 3,691,007 describes an improved method for producing printed circuit board material. Specifically, the method involves pre-coating a conductive metal foil with a porous-polymeric membrane and electro-depositing an electrical resistance layer on the conductive metal through microscopic holes in the polymeric membrane. The polymeric membrane is then removed with a solvent and the resultant bimetal foil laminated to a support layer. The method produces repeatable results from board-to-board and allows all of the resistors on a board to be made to narrow tolerances.
U.S. Pat. No. 3,808,576 describes a printed circuit board material comprising an insulating support layer and electrical resistance material adhered to said support layer and a layer of highly conductive material adhered to the electrical resistance layer. The electrical resistance layer comprises electro-plated nickel alone, or electro-plated nickel together with up to 30% by weight of phosphorus. Additionally, U.S. Pat. No. 3,808,576 describes a novel etching method for the removal of the resistive materials referred to above without the removal of copper which comprises using ferric sulfate and sulphuric acid in aqueous solution. U.S. Pat. No. 3,878,006 discloses an improved etchant for the removal of the resistive material without the removal of copper by use of cuptic sulfate.
Finally, U.S. patent application Ser. No. 06/738,835 describes an improved circuit board material comprising a support layer, at least one electrical resistance material layer, and a conductive material layer adhered to the electrical resistance material layer. The electrical resistance material layer comprises an electro-plated nickel-phosphorus composition wherein at least the top about 10 atomic layers of the electrical resistance material layer are free of sulphur. The electrical resistance material layer described in the referenced application is formed from an electro-plating bath which is essentially free of sulfate ions. Additionally, the referenced patent application describes an electro-plating bath which is substantially free of sulfate and chloride ions which electro-plating bath produces an electrical resistance material layer which is substantially continuous and pit-free and possessed of improved peel strength, resistance change after time, temperature co-efficient of resistance and current noise.
While previous circuit board materials and circuit boards formed therefrom have been found to produce useful products, it is nonetheless desirable to enhance certain aspects of the circuit board stock material and to expand the type of products capable of being manufactured therefrom. It is to this goal and others that the present invention is directed.